12 November 2013
Last updated at 15:21
A team has found a smell receptor in zebrafish that explains their aversion to rotting flesh.
Like zebra fish, humans are also disgusted by the smell of cadaverine, a volatile foul smelling molecule present when meat turns bad.
But other animals that feed on rotting meat – such as bears and rats – find the molecule attractive.
The researchers, writing journal PNAS, say the receptors are vital to help identify toxic food sources.
Humans have millions of olfactory receptors but it remains unclear how many molecules that make up smells interact with the receptors.
Now the one relating to cadaverine has been found.
Sigrun Korsching from the University of Cologne, Germany, said that although many mammals have different smell preferences to humans, the zebrafish’s olfactory systems are similar.
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“The old saying ‘in biology nothing makes sense except in the light of evolution’, I’m pretty sure that’s the same here”
University of Cologne
“It signals danger, if a dead body is lying around maybe the danger is still around. It could also signal that the meat is toxic and should not be eaten,” she told BBC News.
Smell receptors are very powerful, they are present in the nose and are tasked with receiving the smell signals, sort of like an input channel for the nose.
This signal is then evaluated into a meaningful smell by more powerful processes in the brain.
“We have the two pillars of the bridge – the receptor of the peripheral end and the behaviour at the other end, but the bridge in-between, such which neural circuits are activated, we still don’t know, but want to find out next.”
Cadaverine is the product that results when the amino acids in meat become degraded by bacteria. Toxins in the bacteria then infiltrate the meat.
If, like the zebra fish, humans were not naturally repulsed by the smell of cadaverine, they might be more likely to eat bad meat.
Uncovered chicken for example often goes bad before its sell by date, so it’s an extremely helpful sense to have.
The work was on zebrafish but the team says that humans could have a similar neural network.
“It seems to be an innate awareness behaviour for the zebra fish. As far as I know it’s also innate for humans. It’s a case of convergent evolution.” Prof Korsching added.
“The old saying ‘in biology nothing makes sense except in the light of evolution’, I’m pretty sure that’s the same here, even though it’s hard to prove.”
Zebra fish are often used in research, from looking at reversing heart failure to motor neuron disease to developing a treatment for multiple sclerosis.
The zebrafish genome has now also been mapped for the first time in the hope the stripy creatures could help scientists develop cures for a range of human diseases, as their genes mutate in similar ways to human genes.